Optical pyrometers are commonly used to measure temperatures in environments that are too hot to be measured by other temperature measuring devices such as thermometers and thermocouples. Some materials, including graphite and various metals, change color as they are heated, and therefore the temperature of a material can be estimated from the observed color. An optical pyrometer detects the color of an object being heated or the color of a surface in a furnace and correlates this color with a particular temperature. The optical pyrometer is generally mounted at a location where temperatures are not extreme and focused on a portion of a furnace or a material being treated in a furnace to measure color. Some furnaces, for example, may include windows through which a pyrometer can view the color of a material therein. In this manner, very high temperatures can be measured without exposing a measuring device to extreme conditions.
The color measured by a pyrometer is dependent on the material being heated. Therefore, if the pyrometer is focused on a product being processed in a furnace, the relationship between color and temperature for each product processed must be known. To avoid this difficulty and obtain consistent temperature measurements, the pyrometer may be aligned with either a target made of a known material or with a specific portion of a furnace so that repeatable temperature measurements can be obtained.
Some furnace arrangements lend themselves to the mounting of a pyrometer target on a wall of the furnace where the target can remain without interfering with product loading and unloading. Other known furnaces, however, have limited interior space, and therefore any pyrometer target used must be placed in the furnace after the product is loaded into the furnace and removed from the furnace before the product can be removed from the furnace. In one known process, materials to be processed are placed on a pallet, the pallet is placed on a support table having rollers, and the pallet is rolled from support table rollers onto rollers in a furnace. A large and therefore heavy graphite door is placed between the furnace door and the pallet, and the graphite door is then used as a pyrometer target. Smaller targets can be used, but the target must still generally have a large enough targeting area to allow a pyrometer to be readily aimed thereat and be tall enough to provide a temperature reading in a central portion of a furnace away from the furnace floor and to be visible through a window in a furnace door or wall. Since pyrometer targets may be made from dense materials such as steel or graphite, suitable targets are difficult to move. This increases the time required for loading and unloading a furnace and increases the likelihood of worker injury. It would therefore be desirable to provide a system and method for enabling the measurement of a temperature in a furnace that includes a relatively easy to use pyrometer target.